Variable-pitch airscrew for airplanes



Sept. 1, 1942 D. H. BOTTRILL VARIABLE-PITCH AIRSCREW FOR AIRPLANES FiledFeb. 4 1941 3 Sheets-Sheet 1 ATTORNEYS p n. H. BOTI'RILL 2,294,868

' VRIABLE PITCH AIRSCRBW FOR AIRPLANES 3 Sheets-Sheet 2 Filed Feb. 4.1941 m mmuml IAV/lI IIIIIdIIlI f/ III/I INVENTOR P D. H. BOTTRILL2,294,868 VARIABLE-PITCH AIRSCBEW FOR AIRPLANES Filed Feb. 4. 1941 3Sheets-Shee t s INVENTOR v M E ATTORNEYS Patented Sept. 1, 1942 UNITE-DSTATES PATENT orFIc I vxn mntn-m 'r c irffn sonnw non, v A

David H. Bottrill, Montreal, Quebec, Canada, assignor to Canadian Car &Foundry Company Limited, Montreal, Quebec, Canada, a corporationof'Quebec, Canada Application February 4,1941, Serial No. 317,235

'5 Claims. .(Cl. 170162) cally obtained by a manipulation of the enginethrottle differing slightly, if at all, from that which would benormally used in carrying out these maneuvers.

In order that. the invention may be clearly understood-I will describethe airscrew embodying the various features of theinvention which isillustrated in the accompanying drawings:

Figs. 1, 2, 3 and 4, which are on the same scale, show the hub of theairscrew. Fig. 1 is a view looking across the engineshaft, andtheleft-hand side of this figure is sectioned on the plane which containsboth the axis of-the blades and the axis of the engine shaft. Fig. 2 isa view looking lengthwise of the engine shaft showing the hub sectionedon the planewhich contains the axis of the blades and is perpendicularto the axis of the engine shaft. Fig. 3 is a transverse section of the vhub on the plane containing the axis of the engine shaft, and Fig. 4 isa transverse section of the hub on a plane parallel to the axis of theengine shaft and containing the axis of the cam follower.

Fig. 5, on Sheet his a fragmentary section on the line 55 of Fig. 1,showing the adjustable connection between the two sleeves forming theblade spindle.

Fig. 6, on Sheet 1, is a face view of one of the coil springs showingthe spring casing in section.

'Figs. '7 and 8, on Sheet 2, are enlarged views of the cam connecting acentrifugal controlling element with one of the blade spindles. Fig. 7is a face view of the cam, and Fig; 8 is a section on the line 8-8 ofFig. 8.

Fig. 9, on Sheet 2,. illustrates the method by or composition or similarmaterial has at its inner end a cylindrical stub l6 which is fixedlysecured in the inner sleeve 13 by means of a wire thread I'I hereinafterdescribed in detail. The in- 5 ner and outer sleeves are adjustablyconnected by means of a pin l8 seated in half-round longitudinal groovesin'the' inner surface of the outer sleeve and the outer surface of-theinner sleeve. By spacing the grooves of the-inner and outer l0 sleevesslightly differently, as shown in Fig. 5, a

very accurate adjustment of the angular relation between the two sleevesis obtained. The pin I0 is held in the grooves by a cap l9 secured onthe outer end of the tubular extension l2 of the 15 hub. A rotarybearing for the blade spindle is provided between the outer sleeve l4and the hubextension l2, anda thrust bearing 2! is provided between anexternal flange 22 on the inner sleeve l3 of thespindle and an internalflange 2% secured to the body lb of the hub.

As the center of gravity of each blade is necessarily spaced from theaxis of the blade, the .eccentricity of the weight of each blade is balanced by a weight 24 at the outer end of an arm 25 whose inner end isfixed to a short stub shaft 1 26 extending inwardly from the inner endof the blade spindle. The arms 25 pass through slots 21 in the body II!which are wide enough to provide for a turning of each blade spindlethrough'an angle sufficient to move the blades from highpltch positionto low-pitch position, and positively limit the turning of the blades tosuch angle thus insuring that the blades are alyays in an operativeposition. Asa safety factor, the turning of the 3.) two blades may,'ifdesired, be synchronized'by means of a miter gear 28 29 on the arms 25.

A centrifugal controlling element 30 is provided for each blade spindle.Each centrifugal controlling element 30 is slidably mounted in one oftowards and away from the middle of the hub.

Each controlling element 30 carries a springpressed cam follower 34which extends through a slot'35 in the tubular portion to engage a canI0 mounted on the outer sleeve ll of the blade spindle.

The form of the cam 40 carried by each blade spindle is best shown inFigs. 7 and 8. The cam ll) consists of a block which is notched to fit aengaging gear segments end is secured in a hole 52.

notch in circumferential flanges 4| on the outer sleeve l4 of the bladespindle, so that it is held in immovable relation to that sleeve. Thecam contains an endless groove 42 which may have the form of a triangleas shown. The direction in which the cam follower 34 moves around thegroove is indicated by arrows on the groove in Fig. 7. To preventmovement of the follower around the groove in the'opposite direction,the bottom of the groove is provided with ratchet notches 43 havinggradually inclined surfaces 44 which permit the follower to move aroundin the direction of the arrows and abrupt surfaces 45a, 45b and 450which positively prevent backward movement of the cam follower when itis in any one of the three corners a, b and c of the triangular groove.

The centrifugal force on each centrifugal element 3!! is balanced by twospiral springs 48 mounted in spring casings 41 like watch springs andacting on sprockets 48 which engage a double rack 49 attached by a rod50 to one of the centrifugal elements 30. The spiral springs are soadjusted that the centrifugal force of the centrifugal elements 30 holdsthese elements at the outer ends of their ways at maximum engine speedand at an intermediate point at cruising engine speed, while the springshold the elements at the inner ends of their ways at idling speed.

The mounting and adjustment of the blades l5 will next be described.Each blade [5 consists of wood or of a composition such as wood andBakelite, which is softer than metal. The cylindrical stub l6 at theinner end of the blade is groove, preferably having a cross-sectionaldiameter slightly less than the diameter of the wire, is cut in the stubof the blade. One end of the wire is secured in a hole 5| near the innerend of the blade, and the wire is then wound on the blade stub undertension, after which the other A half -round spiral groove is cut in theinner surface of the sleeve ii. The cross-sectional diameter of thisgroove is no greater than that of the tensioned wire. The stub of theblade is then forcibly screwed into the sleeve. The pliability of theexternal thread on the blade makes it possible to screw it into theinternal thread of the sleeve without the clearance which is necessaryin ordinary screw threads, and even with a negative clearance. A verysecure and tight connection between the blade and the sleeve is thusprovided, which has a strength equal to the sheer strength of the woodor a composition of which the blade is made, and which occupies verylittle radial space.

After the blade has been screwed into the sleeve i3 and before the cap[9 is applied to the tubular extension l2, the blade and inner sleeve iiare turned in the outer sleeve l4 until the blade occupies the low-pitchposition best suited to the particular airplane on which the airscrew isto be used. The pin I8 is then inserted in the two grooves of thesleeves II and I4 which are in register when the blade is in thisposition,-and

, the cap I! is applied to hold the pin in position.

engine is idling before the take-off, the springs 44 hold thecentrifugal elements 30 at the inner ends of their ways, that is, in theposition shown in Figs. 1 and 2. The cam follower pin 34 of eachcentrifugal element 30 is then in engagement with the inner corner a ofthe cam groove 42. This holds the blades in low-pitch position.

When the engine is speeded up to its maximum speed in the take-off, thecentrifugal elements 30 move out to the outer ends of their ways. Thestep 45a of each cam groove prevents the cam pin 34 from moving towardsthe corner 0 of the triangular groove 42. Consequently, in the outwardmovement of the centrifugal elements, each cam pin moves along the longside of the groove 42 to the corner b. As the long sides of the camgrooves are parallel to the axis of the blades, the engagement betweenthe cam follower pins and the grooves holds the blades -in low pitchduring the speeding up of the engine. A low pitch for the take-off isthus insured.

After the take-off, the engine speed is cut down by the throttle belowthe normal cruising speed, for example, to half of the maximum speed.This slowing down of'the engine and the airscrew allows-the springs 46to draw the centrifugal elements about half-way inward. In this inwardmovement of the centrifugal elements, the step 45b in each cam grooveprevents the pin 34 from moving back along the long side of the grooveand requires it to move along one of the short sides of the groove tothe' comer c.

In this movement, the engagement between the pins 34 and the cams turnsthe blade spindles so as to place the blades in high-pitch position.This turning is effected by a small force, since the eccentricity of theweight of the blades is balanced by the weights 24 and the load on thethrust bearings 2| is reduced fourfold by the fifty per cent. reductionin speed of rotation. After the blades have been placed in high-pitchposition by reducin the engine speed below cruising speed, each pin isprevented from moving outward by the step 45c. The engine speed may,therefore, be increased as desired without changing the'high-pitchposition of the blades.

When a landing is to be eifected or when for any reason the pilotdesires to place the blades in low-pitch position, it is necessary onlyto cut the speed of the engine momentarily to idling speed. This permitsthe springs 46 to draw the centrifugal elements back to the inner endsof the ways bringing each pin 34 back to the corner a of its cam groove,thus turning the blades to low-pitch position. A landing may be effectedwith the blades in low-pitch position. If, after starting to land, thepilot finds that it is undesirable or unsafe to do so, he canimmediately change to a sharp climb by merely advancing his throttle,since the blades remain in low-pitch position during such speeding up ofthe engine, as explained in connection with the take-off.

Thus the pitch of the blades is always under control of the pilotthrough the pilot's control of the throttle, and the changes of pitchnecessary in taking-off, cruising and landing are made merely bymanipulating the throttle in the same manner as that in which it wouldordinarily be manipulated in these maneuvers.

While the 'airscrew which has been described is entirely adequate forsmall airplanes, my in vention is by no means limited to a two-pitchairscrew. Thus, when my airscrew is used on an airplane of such sizethat it is desirable to provide three pitch positions, it is necessarymerely to substitute for the two-pitch cam shown in Fig. 7 thethree-pitch cam shown diagrammatically in Fig. 10. The three-pitch camhas a step 55:: between the steps 45b and 450 to provide a pitchintermediate between high pitch and low pitch and appropriate forclimbing. Further such steps may be provided on either of the shortsides of the triangular cam groove to provide as many pitch positions asmay be desired.

What I claim is:

1. In an airscrew having a relatively fixed hub element, a tumablymounted blade spindle and a controlling element responsive to speed ofrotation, an interconnection between the controlling element, the bladespindle and the fixed element comprising a cam follower and a cam havingan endless cam groove formed to permit the cam follower to move aroundthe groove in one direction and positively to prevent it from movingaround the groove in the oppsite direction.

2. In an airscrew having a relatively fixed hub element, a turnablymounted blade spindle and a controlling element responsive to speed ofrotation, an interconnection between the controlling element, the bladespindle and the fixed element comprising a spring-pressed cam followerand a cam having an endless cam groove containing ratchet notchespermitting the follower to move periphery 'of a triangular area duringone complete reciprocation of the controlling element and to prevent thecam follower from moving around the periphery of said area in theopposite direction.

4. In an airscrew having a relatively fixed hub element and a turnablymounted blade spindle, a centrifugal controlling elementslidably-mounted on the fixed element for movement parallel to the axisof the blade spindle between inner and outer positions, a spring urgingsaid element towards its inner position, a connection between thecontrolling element and the blade spindle comprising a spring-pressedcam follower and an endless cam groove in the form of a triangle with along side parallel'to the ans of the blade spindle and short sidesinclined to the axis of the blade spindle, the groove containing ratchetnotches preventing the cam follower from moving along the 'longside ofthe triangle when the controlling element moves inwardly from its outerposition 5. In an airscrew having a relatively fixed hub element and aturnably mounted blade spindle; a controlling element slidably mountedon the fixed element for movement parallel to the axis of theblade.spindle, a pair of pinions mounted on the hub element, spiral springsurging said pinions

